﻿232 . . BRITISH FOSSIL CRUSTACEA. 



The Merostomata present a reiteration of the same well-marked characteristics 

 observable in the Podophthalmia and Edriophthalmia, namely, the division into 

 ' brachyuran ' and ' macrouran ' forms, which exemplify well the crawling and swimming 

 types of Crustacea, by the soldering together of the body-segments for strength and 

 compactness in the one, and the retention of free movement of the somites in the other. 



Besides being used as organs of prehension, it is highly probable that the several 

 species of Pterygoti, all of which were furnished with chelate antennas, were males, and 

 that their office may have related to sexual functions. Slimonia, which attains to a very 

 considerable size, has only minute and simple antenna? destitute of chela?. This is also 

 the case apparently in both Eurypterus and Stylonurus. These were perhaps the females. 



3rd. Professor Owen observes : " Pterygotus and Eurypterus resemble Limulus in the 

 organs of vision, save that the facets of the large lateral compound eyes are less distinct 

 or less conspicuous in the fossil." In answer to this we would refer to Pis. XIII and 

 XIX (and woodcut, p. 56) of this Monograph, and to the descriptions of many specimens 

 with the facetted surfaces of the eyes well preserved. Such admirable specimens were 

 not, however, known to the earlier observers. 



We close these notes on modern Limulus with an extract from the admirable Memoir 

 of Professor Alphonse Milne-Edwards, already referred to -- 1 — 



On the Geographical Distribution op Limulus at the Present Day, and 



its Fossil Predecessors. 



Two species of Limulus are found living at the present day, namely, L. moluccanus 

 and L. polyphemus. " One of these, Limulus polyphemus, is confined to the north part 

 of the Atlantic Ocean ; it is found upon the Mexican Coast in the Antilles, and upon the 

 East Coast of the United States, especially Florida and Carolina ; but it is not known 

 elsewhere, and in the adjacent regions it entirely disappears. Limulus reappears very 

 far from these parts, namely, in the islands of Molucca and in the seas of China and 

 Japan, where it presents peculiarities which specifically distinguish it from the Mexican 

 Limulus, but in reality there is only a very slight difference between them, and it seems 

 to me difficult to admit that they were not derived from one primitive stock. In fact, 

 nature never seems to repeat itself in creation, and it is hardly probable that the organic 

 type from which the Limulus of the Jurassic Period was derived, the existing Limulus of 

 the Atlantic Ocean, and that of the Pacific, have no existing ties of kindred between them 

 and are the result of three distinct zoological creations. But at present the Isthmus of 

 Panama, the continents of America, the Arctic Sea, and the Cold Southern Ocean render 

 all communications between the Limuli of the Atlantic and Asiatic regions impossible. 

 It remains therefore to be explained how the descendants of Limulus polypliemus have 

 migrated as far as the seas of Japan and Molucca, where we now find Limulus longispina 



1 "Etudes Anatomiques sur les Limules: Mission Scientifique au Mexique." Paris: 1873, fol. 

 cinquicme partie, p. 4. 



